1. Field of the Invention
The invention relates generally to the field of aligning an x-ray and a visible light beam in a fluoroscope. More particularly, the invention relates to a device containing a radio-opaque material that provides a means to check for precise physical alignment between an x-ray in a fluoroscope and a laser beam in a laser targeting system attached to the fluoroscope.
2. Background Art
Producing and positioning a laser beam that indicates the exact surface point of entry and the precise angle of approach to a subcutaneous structure can be used in many fluoroscopically guided procedures, such as biopsies of deep tissue anatomy, screw, wire and implant placement, vertebroplasty, spinal procedures, arthrograms, selected interventional cardiology, and craniofacial and plastic surgery procedures. In these procedures the laser or other visible light beam usually serves as an accurate visible guide for accessing a subcutaneous structure. Thus, in order to correlate the position of a subcutaneous structure in an x-ray image and the point and direction of entry of a medical instrument on the skin of a patient, it is necessary to achieve the most accurate alignment of an x-ray beam with a visible light beam in a fluoroscopic machine.
The use of a visible light system together with an imaging system to mark or indicate areas of medical interest has been known in the art. For example, U.S. Pat. No. 5,031,203 to Trecha and U.S. Pat. No. 4,117,337 to Staats describe an arrangement where a patient is moved within an imaging system to a predetermined location of a laser system. A method and device for aligning x-rays and a laser beam by aligning x-rays and the bore of a cylindrical device are disclosed in U.S. Pat. No. 4,356,400 to Polizzi et al. A device for aligning a patient at the proper distance from an x-ray source by intersecting two laser beams at a predetermined position is described in British Patent No. GB 2175778A published Dec. 3, 1986. None of these patents discloses a device and method for verifying and perfecting coaxial and coincident alignment between an x-ray and a visible light beam by verifying and correcting alignment of the visible light beam within the source of the visible light beam.
U.S. Pat. Nos. 5,212,720 and 5,644,616 to Landi et al. disclose a technique that uses a calibration device with a marking made of radio-opaque material for coaxially and coincidentally aligning a laser beam with the central ray from an x-ray source.
The techniques of using a radio-opaque material as a marker to mark or encircle a particular area on an x-ray image has been known in the past. For example, U.S. Pat. No. 5,193,106 to DeSena discloses a device for providing percutaneous-based markings in association with x-ray examination procedures. The DeSena patent shows a tape having adhesive backing with a radio-opaque marker made of radio-opaque material affixed to the tape. The radio-opaque marker encloses an area of interest and serves to focus the attention of a podiatrist reviewing an x-ray photograph of the area of interest. U.S. Pat No. 5,565,678 to Manian discloses a system and methods for performing a quantative assessment of the image quality of a radiographic image. A calibration target comprising a stack of circular disks for attenuating an incident beam is employed to form a latent image and ultimately a visible radiographic image to which an examination target may be compared. U.S. Pat. No. 4,698,836 to Minasian discloses a radio-opaque movable ball disposed within a dish shaped opening. The ball is used to record position information on a patient's x-ray film. None of these patents uses a radio-opaque member to verify alignment between an x-ray and a visible light beam in a fluoroscope or any other kind of x-ray equipment. Moreover, none of these patents discloses a method and device for verifying alignment of the visible light beam in the light beam source itself.
The system of aligning an x-ray beam with a visible light beam disclosed in the Landi et al. patents comprises a visible light source with a colinearizer that are attached to an x-ray machine such as a fluoroscope. The colinearizer includes a pair of reticles mounted at each end of the colinearizer. Each reticle has radio-opaque cross-hairs that produce an image of the reticles on a x-ray image. By observing the relative position of the two pairs of cross-hairs on the x-ray image a surgeon or a bio-engineering technician can make a conclusion about the proper alignment of the visible light beam and the central ray of the x-ray beam. Such system and method, however, do not take into account the fact that the visible light beam may deflect from its intended direction inside the colinearizer when, for example, the fluoroscope is moved or when the visible light source is somehow disturbed. In the Landi et al. systems and methods the alignment of the two reticles in the colinearizer with respect to the x-ray does not solve the problem of verifying the alignment of the visible light beam inside the visible light beam source itself. The Landi et al. systems and methods presume that if the colinearizer is aligned with the x-ray beam, the visible light beam will necessarily always be properly aligned with the x-ray. That is not always so, because during the exploit of the x-ray machine the initial alignment between the reticles in the colinearizer and the visible light beam may get lost. Such loss of an alignment will inevitably cause imprecise identification of the point and direction of entry to subcutaneous structures in a patient during a medical procedure.
If a doctor could verify the alignment between the visible light beam and the x-ray as well as between the visible light beam and the source of the visible light beam itself and then print out an image corresponding to the correctly aligned equipment, the doctor would have proof of the fact that he or she operated properly functioning, precisely aligned equipment. Therefore, it would be desirable to have a device and method for verifying alignment of the direction of the visible light beam with respect to the colinearizer in addition to the alignment with respect to the direction of the central ray of the x-ray beam.